“O” Boat Engine rooms

The RFA Service having passed through the Wave, Old Tide and New Tide classes of steam ship from 1945 to 1963 saved the best to the end before all RFA steam ship construction ceased in favour of motor ships. The three ships built in 1965 were easily the best steam RFA’s and possibly some of the best British steam ships ever built. I cannot comment or Resource or Regent as I never went onboard them but I do know they were a totally different animal, Foster Wheeler boilers and English Electric turbines – one wonders why the change from reliable B & W boilers and PAMETRADA turbines successfully used in the New tides and all the additional training necessary for two distinct classes of ship.



At the time the MOD had several major worries about RFA vessels 

Firstly – Reliability:-

the MOD had worries about the reliability and single point of failure of large single diesel engines especially during RAS and the associated problems of spares delivery to the ships worldwide (cylinder liners, pistons weighed many tons). When this was allied with the requirement to spend long times at sea away from any technical support eventually led to the selection of steam for the RFA’s last three large steam fast fleet tankers.

Secondly – Economy:-

all steam ships suffer from the fact that they are external combustion engines having a greater range of losses of efficiency compared with their internal combustion engine (diesel) rivals. For a time in the early/mid 1960’s steam ships became more complex in order to drive down fuel consumption in imaginative (i.e. complex/expensive) ways. The main ways used were 3 and 4 stage feed heating, reheat of super heat steam to use in an intermediate turbine between HP and LP and even pre heating boiler feed water by passing it through the main engine lube oil coolers. All this complexity was intended to bring the consumption down to below the magic figure of 0.5lbs fuel per shaft HP hour. Diesel ships started at less than 0.4lbs fuel per shaft HP hour but had much higher capital costs for the large diesel engine which were usually in the 850 to 1000mm bore range and 8 to 12 cylinders for the same output as turbine ship of say 25 to 30,000 shp and the diesel engine could weigh up to 1000 tons.

Wisely, the RFA chose a middle route through these design options, doubling up on critical equipment as necessary and utilising only two stages of feed heating to save on the necessary complexity. The correct operation of the plant and equipment was essential for safety and the lowest consistent operating costs.

Thirdly – Staff:-

manning the ships was becoming a problem with engineers at a premium (commercial lines offering better pay and conditions) and any solution in the new ships that reduced the need for engineers was investigated.

Problems with the higher running costs of steam ships could be reduced (but never eliminated) and made almost comparable with motor ships (if servicing the additional capital cost of the diesel engine is included) if the engine room staff numbers could be reduced by automation. Additionally, the associated officer and crew accommodation, messing and wardroom of the total build costs would be reduced.

The projected staffing figures were as follows:-


Tideboat                                                           O Boat

Engineer Officers      15                                   Engineer Officers     10

Electrical Officers        2                                   Electrical Officers       2

Firemen/Greasers     23                                   Firemen/Greasers    11

Total                          40                                   Total                          23


Additionally a reduction in catering staff of 2 was anticipated and since the crew numbers were now below 100, no doctor need be carried, total reduction of 20.


Fourthly – Safety in wartime:-

As well as economic operation of the plant and crew reduction, thoughts had also been given to the additional RFA problems of operation in nuclear fallout and this problem could be answered, in part, by plant automation and incorporating a system of bridge control of the main ahead throttle valves.

The existing New Tides gave a good starting point for the new ships, but the result of these additional requirements led to a new design of ship whereby the New Tides’ basic hull was enlarged from 27,000 tons to 33,000 tons, speed increased to 20 knots+ from the Tide’s 17 knots. These changes required an increase in turbine power from 15,000shp to 26,500shp. Larger boiler output was required to match the increased engine output but boiler design had improved in the few years since the New Tides and in fact the boiler size was visually very similar to the New Tides.

In 1964 the idea of automating a complex steam ship was challenging to say the least as electronics were just on the horizon. The bridge control system was designed to slowly increase or decrease the main engine ahead speed. A slow timing was selected to allow all the other automated systems to change as the steam requirements changed.

The automation processes chosen were entirely pneumatic in control and operation and no electronics were used in the original design except in the then revolutionary AEI data logging system. This system recorded up to 213 sensitive points in the engine room and allowed continuous monitoring of one of these points selected by a plug board system on a large mimic diagram.

The controls and indications were led back to a spacious air-conditioned machinery control room (MCR) located at boiler floor level in the watertight bulkhead between the engine room and boiler room.

All engine rooms systems were automated either fully or requiring only minimal human intervention (i.e. boiler burners were inserted and flashed according to demand but only after being initiated by the 4th Engineer and the oil pressure then modulated automatically to maintain steam pressure). Most systems and control loops did not need further adjustment after initial set up except the main boiler turbo feed pumps which had a manually operated bypass that had to be shut above 60 shaft RPM – a round trip of about 80 steps (this was much later automated with a control lever in the MCR)

Sensibly, large hand throttle wheels were also fitted and could also be used instead of the automated bridge control system and, with the engineer’s touch, a much faster response to required speed changes were obtained.

A technical paper was written for the North East Coast Institution of Engineers and Ship Builders in December 1965 by E P Crowdy and H M Pearson entitled “Machinery for Fleet Replenishment Tankers” and some of the detailed specifications, descriptions and photographs from this paper of the main items are shown below.

The main propulsion unit consists of a two cylinder (HP and LP) turbines coupled through a dual tandem, double reduction articulated gear box driving a single four bladed propeller weighing 36 tons at up to 120 rpm. The turbine output required was 26,500shp ahead and 15,600shp astern. This required beefing up the propeller shafting, the intermediate propeller shafting was increased to 23.75 inches diameter and the tail shaft to 29.25 inches diameter in an oil lubricated stern tube.

The two main boilers were of the Babcock and Wilcox Selectable Superheat type with a combined output of 346,000 lbs of steam per hour at 750psig and 950 degrees f. Some 66,000 lbs per hour of this evaporation was de-superheated to 730 psig and 650 degrees f to supply the Steam/Steam generators and other sundry LP services. The boilers are fitted with air puff soot blowers arranged for continuous sequential operation. These comprise 2 retractable lances for the super heater and 10 other localised blowers. Two special high capacity air compressors and 2 large air vessels were provided for this service. The 5 individual burners on each boiler have a turndown ratio of better than 8 to 1 which eliminated the frequent changing of the number of firing burners although all the burners were arranged for remote control from the MCR and one was arranged for remote ignition.

Four 1,500kw turbo alternators are provided which take steam at full boiler pressure and temperature exhausting into self contained condensers. A 500kw diesel alternator is provided for lighting up from dead ship conditions or providing power if the ship shuts down in harbour.

Six turbo cargo pumps at the forward end of the engine room taking full boiler pressure and temperature (2 FFO, 2 Dieso, 2 Avcat). The pumps are so arranged that the hot turbine drive was located in the engine room and the pump end was located in an “L” shaped pump room partially located under the forward end of the engine room. The shaft drive between turbine and pump was through a deck gland seal and bearing eliminating any possibility of hot steam and the pumped oil mixing with the potential of a fire.

The MCR had been specially designed to provide as much information as was necessary for the safe operation, many gauges seen on older ships were not present as the process or operation they represented was fully automated, i.e. lube oil cooler controls, auxiliary steam ring main pressure etc.





The MCR throttle station



The two throttle wheels are evident; these gave a 5 fold increase in change of speed over the fully automated system of bridge control. The ship would appear to be running at 40 shaft RPM as ordered by the bridge RPM telegraph (large dial) and indicated by the lower dial (shaft tachometer) The alternator control panel is on the far left, this allowed the full start up of any or all of the 4 turbo alternators and their switching onto the main switch board.  


The Boiler control panel



The red and green knobs are burner controls, two burners are lit on each boiler, the fuel pressure modulated automatically to give the correct boiler pressure of 750 psig. The small square box on the right and left are the smoke obscuration indicator and alarm for the uptakes, the large box is a steam temperature recorder.

The vertical oblong gauges across the centre are for fan and uptake pressures and any differentials from the norm could be set individually on the lower square boxes.

Fan motor stop and start (high and low speed) are in the foreground, fuel transfer pumps at the far end of the consul.


The Main Turbines from above



The HP turbine is the squareish piece on the right (about 4 ft diameter, 6 ft long) and the smaller square is the HP astern turbine. The box on the left hand side (about 10 ft diameter, 14 ft long) is the LP turbine which has the LP astern turbine within it at the after end. The big pipe going from right to left is the HP exhaust to the LP turbine. The steam pressure in this pipe was about 30 psig (down from 750 psig at the turbine inlet at full power). This pressure was sufficient to run the air pre heaters for the boilers and the two evaporators fed by the two valves shown connecting to the pipe. The drives to the main gear box are the round “pipes” leaving the turbines at the bottom of the photograph.

Forward is to the top of the photo. The turbines and gear box were, of necessity, located many feet below the MCR as were the 4 turbo alternators, diesel alternator, evaporators and other small machinery.

At the lowest level were the feed pumps, circ pumps, F & B, GS, oily water separator and pumps, bilge pumps, fridge circ pimps etc etc. Most had plenty of space around them and the Main Circ pumps were huge each connected to the water box at the ships side with 24” diameter pipe work. It was normal for one to run in sea temps up to 70 degrees f and two to run for higher sea temps. Recirculation happened if the sea temp went below about 65 degrees to keep the condenser circulating water temperature constant.



The Gear Box.


The picture is taken looking aft with the drives into the gear box at the bottom. There was a single flexible drive from each of the HP and LP turbines into the gearbox. To spread the load on the teeth, this then divided into two drive trains and so on to the main wheel.

The three main feed pumps were of the water lubricated type whereby the water at discharge pressure fed the two large PTFE coated shell bearings situated between the turbine and the pump as shown below. No oil was used for lubrication and therefore no possibility of contamination.

This type of pump proved to be remarkably robust and reliable and full power could be achieved (just) on two pumps alone.

The maintenance when required involved stripping both ends off the central casting, removing the innards, replacing the shell type bearings (PTFE coated) and then replacing it all back together.

Space, as ever, was limited and if it were the middle of the three pumps, very hot pieces of metal got in the way of maintenance. I only saw and was involved in one overhaul of one pump in my 3 + years on “O” boats, they were very reliable.






Prop Shaft   Gear Box   Turbines   Feed heating                Boilers                       Alternators


The top photograph above shows the port side of the MCR with the pump state annunciator against the bulkhead in the background and the AEI data logger and mimic diagram to the right hand side.

The photo above shows the mimic diagram. Each measurable point had a jack plug connection for the wandering lead (shown plugged into the air ejector) and alongside each plug in point was an alarm light which lit if the point was outside the set parameters.

The point could be monitored on the 6 digit display beyond the mimic which also had a built in tele-printer to give hard copies for the log or changes of state. 

This equipment was susceptible to temperature and was probably the main reason the MCR was air conditioned, but it worked very well for a 1965 piece of electronics.






The photographs above show the boiler fronts as seen by the 4th engineer in the MCR. The large electric motor is one of two driving the soot blower compressors. On Olna these ran continuously and off and on loaded as the air pressure was used. On Olwen, the compressors stopped and started as the pressure dropped. It was most important to close the valve feeding the pneumatic control equipment and checking that the auxiliary combustion control compressor had cut in (via the annunciator) before commencing sootblowing as a stuck soot blower could drain the air tanks very quickly. The isolating valve is shown prominently on the right foreground.

The 5 burners are shown and are completely controlled from the MCR doing away with dedicated firemen and only one engine room/boiler room greaser was on watch at a time with a 3rd and 4th engineer. Usually only a 4th in harbour. A full shut down was a very rare event.

The lower photo shows the layout of the superheated steam pipes in the boiler and engine room. Because of the pressures and temperatures involved it had been decided to continuously weld all the pipes and valves together, including the Boiler stop and isolating valves and main throttle valves. In doing so, they technically became part of the boiler and had to be hydraulically pressure tested to 1.5 times working pressure.  Special measures had to be taken to support the pipe work which was never intended to take the weight full of water.



The main switch board continued on both sides (back toward the MCR) for non essential services. Ships essential services were on the main panel and could have dedicated alternators and be separate from non essential services needed for RAS.

Most functions on the switchboard could be initiated from the MCR including starting a turbo or diesel alternator.




The HP astern turbine (15,000shp) is at the bottom of the picture. Some of the turbine cover studs are shown around the HP ahead turbine. Because of the high temperature of the steam, expansion would slacken the studs. The studs were made hollow and electrical stud heaters used to heat the studs to above the working temperature and torqued down in the normal way


The LP astern turbine is the section toward the top of the picture


The HP turbine drove into the gearbox via the “Flange” connection between the two large gear wheels on the right of the photo. The drive from these gear wheels on the right went right through the small gear wheels on the large “Bull” wheel and drove back from the “flange” drive coupling on the left. This gave some flexibility to the gear train systems and allowed differential expansion.


The above photo shows the Port main boiler in the builder’s works before installation.



This rather small illustration shows the machinery layout from the side. The MCR is located in the centre of the drawing showing the boilers to the left and the main engines and gearbox below and to the right. The waterline is about MCR level.

The extreme right shows the steam end of the turbo cargo pumps with the pump room underneath



Just to prove a point, hands on the throttle


Peter Maddison